1. Field of the Invention
This invention relates to a process of forming vias in semiconductor structures and in particular to an improved process of forming vias in planarized silicon wafers.
2. Description of the Prior Art
During the manufacture of semiconductor devices, such as transistors and integrated circuits, it has been found necessary to effectuate a planarization or a smooting of the topography of an underlying surface of the structure that is being processed, prior to formation of the vias which enable the electrical connections from the metallization layer. The vias or bonding pads are preferably formed at the locations where the dielectric layer has the largest thicknesses. The semiconductor structure is typically characterized by two distinct areas generally referred to as the field oxide region (FOX) and the diffusion region. However, as a result of the fabrication steps employed in conventional prior art processes, the thicknesses or heights of the dielectric at those regions differ significantly. That is, the distances from the metallization layer to the top surface of the structure are substantially different at the field oxide region and at the diffusion region during etching of the vias. In order to properly etch the thicker regions, the less thick regions are generally overetched. In addition, a problem of undesirable sidewalls, particularly the sidewalls of a second metallization layer, and re-entrant cusps are formed during the process.